Configuring Network Switches for VLAN Tagging

Products

• VMware vSphere ESXi

Issue/Introduction

Why is VLAN not working on my system?

Resolution

If you use ESX Server to route VLAN network traffic, you may need to reconfigure switches attached to your system. Some switches define a "native" VLAN that is used by default. A native VLAN is associated with a particular VLAN ID number. For instance, on a Cisco switch the ID of the native VLAN is 1, by default. Network traffic using the same ID number as a native VLAN may have have the VLAN ID (802.1q) tags automatically removed when routed through the switch, depending on how the switch is configured.

ESX Server requires these ID tags to route traffic in the two VLAN modes supported within the system:

• Virtual switch routing with port groups (switch tagging)
• Virtual machine routing (guest tagging)

Check the configuration of attached switches to ensure that default settings do not interfere with the VLAN modes you have chosen for your server. Switch ports connected to your system must be configured as trunk ports that pass through traffic without removing VLAN ID tags.

You should avoid using a native VLAN when designing the configuration for your external and virtual switches. Using specific ID tags, rather than the default VLAN ID, may prevent networking failures if an external switch is returned to its default settings. Also, avoiding native VLANs provides a more secure interface between virtual machines and your network.

If you are already using a native VLAN, you can reconfigure your switch to pass through ID tags on all ports, including native traffic (that is, messages using the ID of the native VLAN). Set the switch to enable 802.1q tags for all VLAN ID values, either globally or for the trunk ports connected to your system. See the documentation for your switch for details.

For more information about VLANs and ESXi/ESX Servers, see the VLAN Configuration section in the vSphere Networking guide.